1 files changed, 107 insertions, 0 deletions
diff --git a/src/dynamic_load_windows.cpp b/src/dynamic_load_windows.cpp
new file mode 100644
index 0000000..ba8cbcf
--- /dev/null
+++ b/src/dynamic_load_windows.cpp
@@ -0,0 +1,107 @@
+#include <opentracing/dynamic_load.h>
+#include <opentracing/version.h>
+
+#include <windows.h>
+
+namespace opentracing {
+BEGIN_OPENTRACING_ABI_NAMESPACE
+// Returns the last Win32 error, in string format. Returns an empty string if
+// there is no error.
+//
+// Taken from https://stackoverflow.com/a/17387176/4447365
+static std::string GetLastErrorAsString() {
+  // Get the error message, if any.
+  DWORD errorMessageID = ::GetLastError();
+  if (errorMessageID == 0)
+    return std::string();  // No error message has been recorded
+
+  LPSTR messageBuffer = nullptr;
+  size_t size = FormatMessageA(
+      FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM |
+          FORMAT_MESSAGE_IGNORE_INSERTS,
+      NULL, errorMessageID, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+      (LPSTR)&messageBuffer, 0, NULL);
+
+  std::string message(messageBuffer, size);
+
+  // Free the buffer.
+  LocalFree(messageBuffer);
+
+  return message;
+}
+
+namespace {
+class DynamicLibraryHandleWindows : public DynamicLibraryHandle {
+ public:
+  explicit DynamicLibraryHandleWindows(HINSTANCE handle) : handle_{handle} {}
+
+  ~DynamicLibraryHandleWindows() override { FreeLibrary(handle_); }
+
+ private:
+  HINSTANCE handle_;
+};
+}  // namespace
+
+expected<DynamicTracingLibraryHandle> DynamicallyLoadTracingLibrary(
+    const char* shared_library, std::string& error_message) noexcept try {
+  const auto handle = LoadLibrary(shared_library);
+  if (handle == nullptr) {
+    error_message = "An error occurred: " + GetLastErrorAsString();
+    return make_unexpected(dynamic_load_failure_error);
+  }
+
+  std::unique_ptr<DynamicLibraryHandle> dynamic_library_handle{
+      new DynamicLibraryHandleWindows{handle}};
+
+  const auto make_tracer_factory =
+      reinterpret_cast<OpenTracingMakeTracerFactoryType**>(
+          GetProcAddress(handle, "OpenTracingMakeTracerFactory"));
+
+  if (make_tracer_factory == nullptr) {
+    error_message =
+        "An error occurred while looking up for OpenTracingMakeTracerFactory "
+        ": " +
+        GetLastErrorAsString();
+    return make_unexpected(dynamic_load_failure_error);
+  }
+
+  if (*make_tracer_factory == nullptr) {
+    error_message =
+        "An error occurred while looking up for OpenTracingMakeTracerFactory. "
+        "It seems that it was set to nullptr.";
+    return make_unexpected(dynamic_load_failure_error);
+  }
+
+  const void* error_category = nullptr;
+  void* tracer_factory = nullptr;
+  const auto rcode = (*make_tracer_factory)(
+      OPENTRACING_VERSION, OPENTRACING_ABI_VERSION, &error_category,
+      static_cast<void*>(&error_message), &tracer_factory);
+  if (rcode != 0) {
+    if (error_category == nullptr) {
+      error_message = "failed to construct a TracerFactory: unknown error code";
+      return make_unexpected(dynamic_load_failure_error);
+    }
+    const auto error_code = std::error_code{
+        rcode, *static_cast<const std::error_category*>(error_category)};
+    if (error_message.empty()) {
+      error_message = error_code.message();
+    }
+    return make_unexpected(error_code);
+  }
+
+  if (tracer_factory == nullptr) {
+    error_message =
+        "failed to construct a TracerFactory: `tracer_factory` is null";
+    return make_unexpected(dynamic_load_failure_error);
+  }
+
+  return DynamicTracingLibraryHandle{
+      std::unique_ptr<const TracerFactory>{
+          static_cast<TracerFactory*>(tracer_factory)},
+      std::move(dynamic_library_handle)};
+} catch (const std::bad_alloc&) {
+  return make_unexpected(std::make_error_code(std::errc::not_enough_memory));
+}
+END_OPENTRACING_ABI_NAMESPACE
+}  // namespace opentracing